Casting copper chromium steel



Patented Jan. 25, 1944 UNITED STATES PATENT OFFICE CASTING COPPER CHROMIUM STEEL William Pollard Digby, Westminster, London,

England, assignor of one-half to Everard Tuxford Digby, London, England No Drawing.

Application March 25, 1941, Serial No. 385,191. In Great Britain April 9, 1940 Claims.

ing temperature of the molten metal with the rate of-cooling.

I have found that there is a critical temperature at about 1420 to 1440" C. If the molten material is poured into metal moulds at a temperature in excess of this, and allowed to cool slow ly, coarse dendritic crystals are obtained. When poured at temperature below the critical point of 1430i10 C. small polyhedral crystals are obtained especially on rapid cooling.

The pouring temperature is that of the metal as it is actually running into the mould: thismay be determined by optical means, e. g., a radiation pyrometer such as a disappearing filament optical pyrometer.

I secure this rapid cooling when the molten material is poured into metal moulds by proportioning the peripheral length of the ingot to its sectional areathus in a slab ingot having a cross sectional area of six inches by two inches the proportion of the peripheral length per inch length of ingot to cross-sectional area is 2(6+2):-(6 2) or 1.33 to 1, or in the case of a rectangular ingot three inches square is 2(3+3)+(3 3) or again 1.33 to 1;

Such a ratio in the case of metal moulds will ture, if the ingot moulds are allowed to cool in air in the normal manner.

The ingots produced in moulds in which the pouring temperature is as defined above and where the ratio of peripheral length in inches to cross sectional area in square inches is unity or in excess thereof maybe forged or rolled without reheating and annealing prior to soaking and heating for forging or rolling.

When, however, the ratio of the peripheral length to the cross-sectional area is less than unity as in the case of an ingot six inches square where the ratio is 0.66 to l, or in the case of an ingot 9 inches square where the ratio is 0.33 to 1, the formation of dendritic crystals or of very coarse polyhedral crystals may be further checked by stripping the mould as soon as is convenient while the metal in the mould is still at a red heat, say 900 to 1000 C. or pouring the molten metal into a copper mould which is water-jacketed.

When the molten metal is poured into a waterjacketed copper mould the ratio of peripheral length in linear inches to the cross-sectional area in square inches may be under 0.7 to 1.0 without risk of the formation of large dendritic crystals or very coarse polyhedral crystals.

Ingots produced in moulds in which the pouring temperature is as defined above and wherethe ratio of theperipheral length to the crosssectional area. is less than unity should preferably be slowly reheated to 950 to 970 C. and slowly cooled in the furnace prior to soaking and heating for forging or rolling.

Rectangular and slab ingots prepared in this manner do not require unidirectional working when hot as .is the case where long dendritic crystals are formed.

Where a hollow ingot or billet of annular cross? section is used for extrusion into hollows for pipes or cylinders the molten metal is poured 4 into an ingot mould having a hollow core, which core is cooled during and subsequently to.the

- give a mass ofmetal of a fine polyhedral strucpouring of the metal by means of a blast of compressed air.

In ordinary steels where a coarse crystal structure can be reduced by heat treatment, the pouring temperature is not regarded'as of vital importance provided the temperature is high enough to have the requisite fluidity and low enough to avoid the burning of the metai.

In the chrome copper steels of the proportions stated the initially visible structure appears to be congenital and only admits of reduction by hot working and not by heat treatment.

It is an advantage to paint the inside of the metal mould with an aluminium paint instead of a graphitic or bituminous one.

The pouring temperatures defined above are also important in the case of a sand casting having parts of one'inch in thickness and over, but are not so important in the case of the castings where there is an immediate chilling effect from the sand. Stripping assoon as set is again advisable, as alsothe painting of the'suriaces of the mould with an aluminium paint.

Example nese, 0.2% silicon and the balance iron, was

ingot having smaller crystals which was -forged easily.

The third sample according to the invention is thus much easier to forge and the advantage is exaggerated when rolling sheets or bars of the material.

In general I find that ingots poured at 1430 C. and rapidly cooled can be rolled easily, with minimum waste and in some cases yielding a better product whereas an ingot having a coarse structure. such as is obtained by pouring at 1470" C. or upwards and slowly cooling, is difiicult to roll, as cracking is liable to occur in the early stages of rolling or working.

I declare that what I claim is:

l. The process of casting a steel alloy containing from 5 to 25 per cent. of copper and from to 30 per cent. of chromium. which consists in pouring the molten metal into a. mold in which the peripheral length in inches of the ingot is at least equal to its cross sectional area in square inches, the poured metal being at a. temperature below the critical point of 1430 degreesilO degrees C.. and rapidly cooling the poured metal to below 1000 degrees (3. whereby to effect the production only of fine polyhedral crystals in the ingot.

2. The process of making an article from a steel alloy casting containing from 5 to per cent. of copper and from 10 to per cent. of chromium, which consists in pouring the 'molten metal into a mold while the poured metal is at a temperature below the critical point of 1430 degrees 0.110 degrees C.-, rapidly cooling the poured metal to below 900 degrees C. whereby to effect the production only of fine polyhedral crystals in the ingot, reheating to about 950-970 degrees 0., slowly cooling to obtain a machinable casting, reheating and mechanically working thecasting to produce an article therefrom.

3. The process of casting a steel alloy containing from 5 to 25 per cent. of copper and from 10 to 30 per cent. of chromium, which consists in pouring the molten metal into a mold having a hollow core while positively cooling the core, the poured metal being at a temperature below the critical point of 1430 degreesilO degrees C., and rapidly cooling the poured metal to below 1000 degrees C. whereby to eflect the production only of fine polyhedral crystals in the ingot. 4

4. The process of casting a steel alloy contain ing from 5 to 25 per cent. of copper and from 10 to 30 per cent. of chromium, which consists in pouring the molten metal into a mold while the poured metal is at a temperature below the critical point of 1430 degrees C. +-10 degrees C., and rapidly cooling the poured metal to a temperature below 1000 degrees C. whereby to effect the production only of fine polyhedral crystals in the inget, before mechanical working thereof.

5. The process of making an article from a steel alloy casting containing from 5 to 25 per cent. of copper and from 10 to 30 per cent. of chromium, which consists in pouring the molten metal into-a mold while the poured metal is at a temperature-below about 1440 degrees 0., rapidly cooling the poured metal to a temperature below 1000 degrees C. before mechanical working thereof whereby to obtain acasting having a fine polyhedral structure, and mechanically working said casting to form an article.

W. P. DIGBY. 

